Uniqueness of acoustical patterns for Normal, Rheumatoid and degenerative knee joint diseases has been established in previous studies. The present study seeks to improve the understanding of the mechanism of the sound "source" inside the diseased knee joint by both in-vitro and in-vivo modeling. In-vitro modeling involves the "sounding" of bovine joints which are systematically destroyed by both mechanical and chemical menas. In in-vivo modeling both rheumatoid and degenerative diseases are first induced in rabbits' knee joints, using chemical and surgical techniques. These are then "sounded" and sacrificed for visual inspection.